1. Field of the Invention
The present invention relates, in general, to rotary shaving cutters for finishing gear teeth.
2. Description of the Art
The use of rotary shaving cutters for finishing gear teeth previously formed by a hobbing or shaping operation has been known for quite a long time. Such shaving cutters typically have a circular array of radially extending teeth, with the cutting edge profile of each tooth lying in a plane, in one arrangement perpendicular to the bore axis between opposite sides of the shaving cutter. Each cutting edge profile is formed at the intersections of a land surface and an adjacent serration surface. FIG. 10 shows one tooth of a prior art shaving cutter 90. The tooth 90 includes cutting edge profiles 96 formed by land surfaces 92 and serration surfaces 94 equally spaced along the face width of the tooth 90.
The profile of the cutting edges of each tooth of a shaving cutter will have a conjugated shape to the desired profile of the teeth of the work gear to be shaved. Usually, the work gear is driven by the shaving cutter in a tooth-to-tooth meshing relationship at skewed axes. The entire shaving operation is done through the entire face width of the work gear by either reciprocating the work gear across the shaving cutter with parallel or diagonal motion or just by plunging the work gear into the wider plunge-type shaving cutter.
Such shaving cutters are typically formed as a one-piece body with the serrated teeth being shaped one side at a time for each complete tooth. This process requires two accurate machine set-ups for each shaving cutter and long shaping operations to produce the finished shaving cutter.
It is well known in the cutting tool art that the life of a shaving cutter depends on how smoothly the surface finish of the cutting edges can be formed. When the teeth of a shaving cutter become worn due to repeated cutting of work gear teeth, it is necessary to re-sharpen the shaving cutter teeth to restore the sharpness of the cutting edges. Typically, a grinding wheel is passed along the shaving cutter tooth spaces to remove material stock from the tooth flanks to resharpen the cutting edges. However, due to the roughness of the serration surface, i.e., the serration surfaces 94 of the prior art shaving cutter shown in FIG. 10, the cutting edge profiles 96 after the resharpening operation may not be smooth enough to shave the expected number of work gears. As a result of this poor performance, the cost per work gear produced by a single shaving cutter may tangibly increase.
The life of a conventional shaving cutter varies between 2,000 and 10,000 parts per resharpening. The upper limit on the number of parts capable of being formed by previously devised shaving cutters between resharpenings is limited by the manner in which the grooves of the shaving cutters are manufactured. Even in previously devised shaving cutters formed of a plurality of individual plates which are fixedly joined together on an axially extending body, the cutting edges formed on alternating plates have been carefully manufactured, but little attention has been played to the surface finish of the plates themselves. For long life and strength, such plates are typically hardened after being initially stamped or otherwise formed to the desired dimensional shape. However, as is well known, such hardening introduces variations or distortions in such plates which results in a tolerance buildup over the length of the shaving cutter which can lead to inaccuracies in finishing a gear. While such tolerance buildup due to variations in the thickness of each plate is less of a problem in a spur shaving cutter, such variations create a more significant problem in a helical shaving cutter. The tolerance buildup caused by varying thickness cutting and spacer disks can vary the helical arrangement of the cutting teeth along the length of the cutter and thereby if used as it is would lead to significant inaccuracies in the finished gear teeth. To correct this problem, it may require long grinding stock time of the teeth profile and the possible elimination of the serration cutting edge depth in the shaving cutter. Applicant has uniquely discovered that the better the surface finish on the faces of the plates of a wafer-type shaving cutter as well as a surface finish on the major faces of the teeth on each plate, the longer the useful life of the shaving cutter between resharpenings.
It would be therefore desirable to provide a shaving cutter which overcomes the problems of previously devised shaving cutters. It would also be desirable to provide a shaving cutter which enables a smooth surface finish to be easily provided on the cutting edges of the shaving cutter teeth so as to increase the usable life of the shaving cutter between re-sharpening operations. It would also be desirable to provide a shaving cutter which can be more easily manufactured than previous shaving cutters. It would also be desirable to provide a shaving cutter which enables virtually any angle to be formed in the cutting edges of the shaving cutter teeth. It would also be desirable to provide a shaving cutter whose cutting edges can be titanium nitride or titanium carbide coated to further increase the life of the shaving cutter between re-sharpenings. It would be desirable to provide a shaving cutter which has symmetrical cutting edges on each tooth to equalize cutting pressure on each tooth of a work gear so as to improve the surface finish and smooth cut of a work gear. Finally, it would be desirable to provide a shaving cutter in which a smooth surface finish is formed on each plate for constant plate thickness along the axial length of the shaving cutter.